Action: Reintroduce primates into habitat with predators

Key messages

Two before-and-after studies in Brazil found that most golden lion tamarins reintroduced into habitat with predators, alongside other interventions, did not survive over one to seven years but reproduced succesfully.

Three studies, including two before-and-after studies, in the Congo, The Gambia and Guinea, found that most chimpanzees reintroduced into habitat with predators, alongside other interventions, survived over one to five years or increased population numbers. One before-and-after study in Gabonfound that most western lowland gorillas reintroduced into habitat with predators, alongside other interventions, survived over nine months.

One before-and-after study in Madagascar found that most black-and-white ruffed lemurs reintroduced into habitat with predators did not survive over five years. One study in Madagascar found that all reintroduced lemurs survived over 30 months after being released into habitat with predators, along with other interventions.

One study in Gabon found that most mandrills reintroduced into habitat with predators, alongside other interventions, survived over 30 years.

Two before-and-after studies in South Africa found that most vervet monkeys reintroduced into habitat with predators, alongside other interventions, survived over six months.

Two studies, including one before-and-after study, in Vietnam and Indonesia found that most lorises reintroduced into habitat with predators, alongside other interventions, were assumed dead within approximately one year after being released.

Supporting evidence from individual studies

1

A before-and-after trial in 1954–1985 in a rainforest in Poço das Antas Reserve, Brazil found that translocation, alongside nine other interventions, led to a decline within one year of the population of captive-born golden lion tamarin Leontopithecus rosalia released into habitat with natural predators. No statistical tests were carried out to determine whether this decrease was significant. Of the 14 individuals released, seven died and two were removed. Three infants were born, one of which died due to illness. Eight individuals were released as a family group and six individuals were released as pairs one month later. Tamarins were placed in enclosures measuring 15 x 4.5 x 3 m to acclimatize. Tamarins were habituated to humans and fostered to aid survival in the wild. Sick or injured tamarins were captured and treated in a nearby rehabilitation centre. Reintroduced tamarins were supplied with food for ten months after their release. Artificial nesting boxes, which were hollow logs provided to tamarins during training, were also set up in the reserve. The study does not distinguish between the effects of the different interventions mentioned above.

2

A before-and-after trial in 1984–1991 in coastal forest in Poço das Antas Reserve, Brazil found that the majority of golden lion tamarins Leontopithecus rosalia that were reintroduced into habitat with predators along with 14 other interventions, did not survive over seven years. Fifty-eight of 91 (64%) reintroduced tamarins did not survive in the wild. Over seven years 57 infants were born (reproductive rate=63%) of which 38 (67%) survived. Six reintroduced tamarins were killed by predators, but none of the wild-born offspring fell prey to predators. Different groups of captive-bred or orphaned tamarins were introduced in different years into habitat where the species was already present. All tamarins were quarantined, underwent veterinary checks and were treated for parasites before release. Reintroduced sick or injured animals were rescued, treated and re-released. Some groups were trained in behaviours that would aid their survival, provided with supplementary food, water and nesting boxes, and allowed to adapt to local habitat conditions before release. The reserve forest was officially protected in 1983. The study does not distinguish between the effects of the different interventions mentioned above.

3

A before-and-after trial in 1996–2001 in a tropical forest in Conkouati-Douli National Park, Republic of Congo found that the majority of 36 wild-born orphan chimpanzees Pan troglodytes troglodytes that were reintroduced into habitat with predators along with other interventions, survived for at least 1-5 years. Twenty-six of 36 chimpanzees survived and only three were confirmed dead, of which none were reported to have been killed by predators. The remaining seven chimpanzees disappeared, resulting in a minimum survival rate of 72%, with a possible 92%. One infant, whose parents were both released in 1996, was born in 2001. Chimpanzees were rehabilitated on islands before their introduction into habitat already occupied by wild chimpanzees. After release, individuals were equipped with radio transmitters and followed regularly by local staff to record data on cycling status, interactions with resident wild chimpanzees, and sexual behaviour. Parentage was determined by analysing DNA extracted from hairs of all released chimpanzees and infants. Injured chimpanzees received veterinary care. The study does not distinguish between the effects of the different interventions mentioned above.

4

A before-and-after trial in 1997–2002 in forest in Betampona Reserve, Madagascar found that less than half of all captive-bred, parent-reared black-and-white ruffed lemurs Varecia variegata variegate that were reintroduced into habitat with predators along with ten other interventions, survived for five years. Five of 13 individuals (39%) survived in the wild and six (46%) individuals were born, of which only four survived. One female and one male of the group reproduced and the male became fully integrated into the wild group. One male and one female were killed by a predator. Before release lemurs were allowed to adapt to local habitat conditions. All released animals were fitted with radio transmitter collars for post-release monitoring. Captive lemurs had limited semi-free-ranging experience, were quarantined, and underwent veterinary screens before their reintroduction in groups into habitat where the species was already present. Lemurs were recaptured and treated when sick and provided with supplementary food and water. Dead lemurs were detected and their cause of death determined. The study does not distinguish between the effects of the different interventions mentioned above.

5

A study in 1979–2004 in tropical forest in River Gambia National Park, The Gambia found that rehabilitated western chimpanzees Pan troglodytes verus that were reintroduced into habitat with small populations of natural predators, alongside other interventions, increased from 50 to 69 chimpanzees over 25 years. No statistical tests were carried out to determine whether this increase was significant. Fertility and mortality rates were similar to wild chimpanzee populations, except for infant mortality (18%), which was lower. Time between births, average age at first birth, proportion of males at birth, age at first sexual swelling in females, and adolescent infertility, were similar to wild chimpanzees. In total, 50 chimpanzees were released on three islands. Individuals were reintroduced in groups and into habitat with no wild or previously reintroduced chimpanzees. Chimpanzees were provided supplementary food daily or every second day, depending on which one of the islands they lived on. Individuals received periodic deworming, and were given antibiotic treatment when they suffered from severe colds. The study does not distinguish between the effects of the different interventions mentioned above.

6

A study in 2002–2006 in tropical forest in Lékédi Park, Gabon found that around one third of captive-bred mandrills Mandrillus sphinx that were reintroduced into habitat with predators along with other interventions, died within one year. Mortality was 33% (12/36), with dependent infants being most affected. Fertility rate was 42% (5/12 females), where two of the five infants survived for longer than six months. Mortality decreased to 4% in the second year and fertility rate remained at 42%, but all five infants born survived for at least six months. Their range remained limited during the first two years after release. Mandrills were reintroduced as a group into habitat already occupied by the species. Before release mandrills were allowed to adapt to local habitat conditions, and were treated for endoparasites. Mandrills received supplementary feeding until 2005. The study does not distinguish between the effects of the different interventions mentioned above.

7

A before-and-after trial in 2006–2007 in rainforest in Analamazaotra Special Reserve, Madagascar found that habituated black-and-white ruffed lemurs Varecia variegata variegata and diademed sifakas Propithecus diadema survived for at least 30 months and reproduced after they were translocated from disturbed sites to undisturbed habitat with natural predators along with other interventions. No deaths of black-and-white ruffed lemurs were recorded over a 30-month observation period and one diademed sifaka died from natural causes. Four sets of black-and-white ruffed lemurs (reproductive rate=57%) and seven diademed sifaka infants were born (reproductive rate=26%), the latter of which only two survived. Two to eight months before a translocation was carried out, lemurs were darted and underwent veterinary checks. Released primates were habituated to human presence and relocated and monitored with the aid of radio-collars. A total of seven black-and-white ruffed lemurs and 27 diademed sifakas were captured at four disturbed forest sites and released in their social units to the reserve where the species had become locally extinct. The study does not distinguish between the effects of the different interventions mentioned above.

8

A before-and-after trial in 2008–2010 in dry forest in Haut Niger National Park, Guinea found that the majority of wild-born orphaned western chimpanzees Pan troglodytes verus that were reintroduced into habitat with predators, along with other interventions, survived reintroduction and remained free-living for at least 27 months. One of 12 released chimpanzees died after failing to recover from anaesthesia during a recovery mission. One female returned to the sanctuary voluntarily and one male was returned after suffering injuries during another recovery mission. Five chimpanzees remained together at the release site and two infants were born both of which survived. Another female immigrated into a wild chimpanzee community and three chimpanzees moved to an area away from the release site. Although predators are present in the forest no observations of attacks on chimpanzees were made. Before release chimpanzees were screened for diseases and some chimpanzees were allowed to acclimatize to local habitat conditions. Chimpanzees were initially supplemented with food on a daily-, and later on, a weekly basis. The study does not distinguish between the effects of the different interventions mentioned above.

9

A before-and-after trial in 2009–2010 in coastal Ngume Forest, South Africa found that more than half of the captive, wild-born vervet monkeys Chlorocebus aethiops that were reintroduced into habitat with predators, survived for at least six months after release. Three of the 16 reintroduced monkeys (19%) were reported dead. Of these, two were killed by natural predators and one by hunting dogs Canis lupus familiaris. Four individuals (25%) went missing. One infant was born two weeks after release. Monkeys were introduced as a troop of 16 individuals into habitat where the species was absent. To acclimatize, monkeys spent one day in a release enclosure (49 m2). Monkeys were provided supplementary food twice a day for two weeks and once a day for a further three weeks after release. The release site was nationally protected. The study does not distinguish between the effects of the different interventions mentioned above.

10

A before-and-after trial in 2008 in a coastal forest in Isishlengeni Game Farm, Kwazulu-Natal, South Africa found that that over 60% of rehabilitated vervet monkeys Chlorocebus aethiops that were reintroduced into habitat with predators, along with other interventions, survived for at least six months. Five of 29 introduced individuals (17%) were killed by predators. Six individuals (21%) went missing. No females reproduced. Monkeys were introduced as a troop of 29 individuals into habitat already occupied by the species. To acclimatize, monkeys spent two nights in a release enclosure (49 m2). Monkeys were provided with supplementary food. Medical care was provided when necessary before release and while housed at the nearby rehabilitation centre. The study does not distinguish between the effects of the different interventions mentioned above.

11

A site comparison in 2008–2012 in two forests in Dao Tien Island (DTI) and mixed forest in Dong Nai Biosphere Reserve (DNBR), south Vietnam found that hyalf of pygmy slow lorises Nycticebus pygmaeus that were released into habitat with predators, along with eight other interventions, survived for at least two months. Four out of eight lorises survived for at least two months after release, whereas the remaining lorises died or their radio-collar signal was lost. Both release sites were protected and no wild resident lorises occurred there. Lorises were released during the wet season after all of them had undergone a 6-week quarantine, veterinary screens and treatment for parasites. Lorises were kept in a cage for between two days and two months, and were fed supplementary food for seven or 30 days. Bodies of dead animals were examined to determine their cause of death. The study does not distinguish between the effects of the different interventions mentioned above.

12

A site comparison in 2008–2012 in two forest sites in Cat Tien National Park, Vietnam found that all pygmy slow lorises Nycticebus pygmaeus that were released into habitat with predators along with other interventions either died or disappeared. Three of five reintroduced lorises were killed by predators and the radio collar signal of two lorises was lost at an early stage after release. Before release all lorises underwent a 6-week quarantine, veterinary screens, and treatment for parasites. Lorises were released into habitat with no resident wild lorises. Three lorises were released during the dry season. Another two individuals were held in a semi-wild enclosure for one month to foster behaviour that would facilitate their survival in the wild, and then released during the wet season. Bodies of dead animals were examined to determine the cause of death. The study does not distinguish between the effects of the different interventions mentioned above.

13

A before-and-after trial in 2006–2011 in tropical forest at Gunung Halimun Salak National Park and Batutegi Nature Reserve, Indonesia found that few reintroduced Javan slow lorises Nycticebus javanicus and greater slow lorises N. coucang that were released into habitat with predators along with other interventions, survived for at least 146 and 22-382 days, respectively. One of five reintroduced greater slow lorises survived for at least 146 days and five of 18 reintroduced Javan slow lorises, survived for at least 22-382 days. Three greater slow lorises were killed by predators. Before release, lorises underwent quarantine and veterinary screens. Sick individuals were recaptured and treated. Twenty-one lorises were held in enclosures at the release site to adapt to local habitat where wild individuals occurred. Bodies of dead lorises were examined to determine their cause of death. The study does not distinguish between the effects of the different interventions mentioned above.

14

A before-and-after trial in 2008–2010 in a tropical forest in Batéké Plateau National Park, Gabon found that the majority of western lowland gorillas Gorilla gorilla gorilla that were reintroduced into habitat with predators along with ten other interventions, survived for at least nine months. Four of five juvenile gorillas survived for at least nine months after release. One juvenile was killed by a wild chimpanzee. Before reintroduction chimpanzees spent the night in an enclosure equipped with nesting platforms, nesting material, supplementary food and water. Three captive-bred and two orphaned wild born individuals were reintroduced as a group into habitat where the species was absent. Gorillas were dewormed regularly on-site. Caretakers guided gorillas into different forest patches on a daily basis. The study does not distinguish between the effects of the different interventions mentioned above.

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Effectiveness

An assessment by independent experts of the effectiveness of this action based on the summarized evidence (0% = not effective, 100% = highly effective). This score is based on the direction and size of the effects reported in each study. Actions with high scores typically have large, desirable effects on the target species/habitat in each study. There is some variation between actions, e.g. 100% effectiveness in adding underpasses under roads for bat conservation will likely have different impacts to 100% effectiveness in restoring marsh habitat. The effectiveness score does not consider the quantity or quality of studies; a single, poorly designed study could generate a high effectiveness score. The effectiveness score is combined with the certainty and harms scores to determine the overall effectiveness category (for more details see https://www.conservationevidence.com/content/page/79).

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An assessment by independent experts of the harms of this action to the target group of species/habitat, based on the summarized evidence (0% = none, 100% = major undesirable effects). Undesirable effects on other groups of species/habitats are not considered in this score. The harms score is combined with the effectiveness and certainty scores to determine the overall effectiveness category (for more details see https://www.conservationevidence.com/content/page/79).

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The overall effectiveness category is determined using effectiveness, certainty and harms scores generated by a structured assessment process with multiple rounds of anonymous scoring and commenting (a modified Delphi method). In this assessment, independent subject experts (listed for each synopsis) interpret the summarized evidence using standardised instructions. For more details see https://www.conservationevidence.com/content/page/79.